Refrigeration & Air-Conditioning Practice Set-3

May 18, 2021

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1. Highest temperature encountered in refrigeration cycle should be

Near critical temperature of refrigerant

Above critical temperature

At critical Temperature

Much below critical temperature

2. A reversible engine has ideal thermal efficiency of 30%. When it is used as a refrigerating machine with all other conditions unchanged, the coefficient of performance will be

1.33

2.33

4.33

3.33

3. Most thermostatic expansion valves are set for a superheat of

10°C

20°C

5°C

15°C

4. The vapour compression refrigerator employs the following cycle

Reversed Rankine

Rankine

Carnot

Reversed Carnot

5. When the temperature of the surrounding is higher than the temperature of the body, then the heat loss by convection from the body to the surrounding will be

None of these

Negative

Zero

Positive

6. The freezing point of sulphur dioxide is

-75.2°C

-77.7°C

-135.8°C

-56.6°C

7. The operating pressure for refrigerating units using R-12 as a refrigerant is

2 bar

15 bar

8 bar

30 bar

8. For obtaining high COP, the pressure range of compressor should be

High

Optimum

Any value

Low

9. In a flooded evaporator refrigerator, an accumulator at suction of compressor is used to

Collect liquid refrigerant and prevent it from going to compressor

Detect liquid in vapour

Collect vapours

Superheat the vapour

10. Which of the following statement is correct?

(B) The increase in air movement increases the evaporation from the human body.

(A) The human body can lose heat even if its temperature is less than the atmospheric temperature.

(D) Both (A) and (B)

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11. The general rule for rating refrigeration systems (excepting for CO₂ system) is to approximate following h.p. per ton of refrigeration

0.1 to 0.5 h.p. per ton of refrigeration

2 to 5 h.p. per ton of refrigeration

1 to 2 h.p. per ton of refrigeration

0.5 to 0.8 h.p. per ton of refrigeration

12. In a lithium bromide absorption refrigeration system

None of these

Lithium bromide is used as a refrigerant and water as an absorbent

Ammonia is used as a refrigerant and lithium bromide as an absorbent

Water is used as a refrigerant and lithium bromide as an absorbent

13. A human body feels comfortable when the heat produced by the metabolism of human body is equal to the

(D) Difference of (A) and (B)

(B) Heat stored in the human body

(A) Heat dissipated to the surroundings

14. In a refrigeration system, the expansion device is connected between the

Receiver and evaporator

Condenser and receiver

Compressor and condenser

Evaporator and compressor

15. The boiling point of ammonia is

-77.7°C

-33.3°C

-10.5°C

-30°C

16. The change in evaporator temperature in a refrigeration cycle, as compared to change in condenser temperature, influences the value of C.O.P.

Unpredictable

Equally

Less

17. The minimum temperature to which water can be cooled in a cooling tower is

Ambient air temperature

Dew point temperature of air

Wet bulb temperature of air

Dry bulb temperature of air

18. Critical temperature is the temperature above which

Water will evaporate

A gas will immediately liquefy

A gas will never liquefy

Water will never evaporate

19. In a refrigeration system, heat absorbed in comparison to heat rejected is

Less

More for small capacity and less for high capacity

Same

20. On the pressure-enthalpy diagram, condensation and desuperheating is represented by a horizontal line because the process

Takes place at constant temperature

Involves no change in volume

Takes place at constant entropy

Takes place at constant pressure

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21. Which of the following is not a desirable property of a refrigerant?

High risibility with oil

Good electrical conductor

Low boiling point

Large latent heat

22. The value of C.O.P in vapour compression cycle is usually

Always more than unity

Always less than unity

Any one of the above

Equal to unity

23. If a heat pump cycle operates between the condenser temperature of +27°C and evaporator temperature of -23°C, then the Carnot COP will be

0.2

1.2

24. Which of the following cycles uses air as the refrigerant?

Carnot

Ericson

Stirling

Bell Coleman

25. In actual air-conditioning applications for R-12 and R-22, and operating at a condenser temperature of 40° C and an evaporator temperature of 5° C, the heat rejection factor is about

1.25

2.15

5.12

26. Cooling water is required for following equipment in ammonia absorption plant

Condenser

Absorber

Evaporator

Condenser, absorber and separator (rectifier)

27. The curved lines on a psychrometric chart indicates

Dry bulb temperature

Dew point temperature

Wet bulb temperature

Relative humidity

28. A certain refrigerating system has a normal operating suction pressure of 10 kg/cm gauge and condensing pressure of about 67 kg/cm. The refrigerant used is

Brine

Carbon dioxide

Freon

Ammonia

29. The domestic refrigerator uses following type of compressor

Axial

Miniature sealed unit

Centrifugal

Piston type reciprocating

30. Freon group of refrigerants are

Inflammable

Nontoxic and non-inflammable

Non-inflammable and toxic

Toxic

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31. Mass flow ratio of NH₃ in comparison to Freon-12 for same refrigeration load and same temperature limits is of the order of

9: 1

1: 9

1: 3

1: 1

32. The C.O.P. of a refrigerator working on a reversed Carnot cycle is (where T₁ = Lowest absolute temperature, and T₂ = Highest absolute temperature)

(T₂ - T₁)/T₁

T₁ / (T₂ - T₁)

T₂/ (T₂ - T₁)

(T₁ - T₂)/T₁

33. A thermostatic expansion valve in a refrigeration system

Maintains different temperatures in evaporator in proportion to load

Is suitable only for constant load systems

Ensures the evaporator completely filled with refrigerant of the load

None of the above

34. The refrigerant after condensation process is cooled below the saturation temperature before throttling. Such a process is called

Super-cooling

None of these

Sub-cooling or under-cooling

Normal cooling

35. The atmospheric air at dry bulb temperature of 15°C enters a heating coil maintained at 40°C. The air leaves the heating coil at 25°C. The bypass factor of the heating coil is

0.4

0.6

0.67

0.376

36. The bank of tubes at the back of domestic refrigerator is

Capillary tubes

Condenser tubes

Evaporator tubes

Refrigerant cooling tubes

37. Rating of a domestic refrigerator is of the order of

40 tons

5 tons

10 tons

0.1 ton

38. The condition of refrigerant after passing through the condenser in a vapour compression system is

Dry saturated vapour

Saturated liquid

Wet vapour

Superheated vapour

39. A bootstrap air cooling system has

Two heat exchangers

Four heat exchangers

One heat exchanger

Three heat exchangers

40. The capillary tube, as an expansion device, is used in

Domestic refrigerators

Room air conditioners

Water coolers

All of these

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A Demrot is the founder of VideRime Online Learning, a leading engineering website. He did his BE Civil and M.Tech Structure from RGPV University, Bhopal and has been working as an Assistant Professor in a reputed college.

Refrigeration & Air-Conditioning Practice Set-3

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